The invention relates to a control method for controlling an adjusting system of a disc brake having a caliper which reaches over a brake disc axially displaceable on a wheel axle, having brake pads arranged on each side of the brake disc, having an application device for the application of the disc brake, and having the electromotively designed adjusting system, which can be controlled by way of the control device. The adjusting system has at least one adjusting device, respectively, on each side of the brake disc. The adjusting device has an electric motor for adjusting the brake pads when brake pad wear occurs. The control method is implemented via a program of the control device. The invention also relates to a brake disc assembly.
Disc brakes with an electromotively operated adjusting system are known per se; thus, for example, from German Patent document DE 197 56 519 A1. A center arrangement of the adjusting drive between the rotating screws or adjusting screws is also known; for example, from German Patent document 37 16 202 A1 or International Patent document WO 99/05428.
International Patent document WO 99/05428 also describes a particularly simple control method, which can be implemented without additional sensors. For this purpose, it is suggested to carry out the release play adjustment after each braking or after a defined fixed number of brakings.
It is problematic that the known disc brakes either require a high-expenditure sensor system for measuring the release play or that a jamming of the disc brake may occur when a braking is initiated during the adjusting of the release play.
It is therefore an object of the invention to create a reliable control method for adjusting systems of disc brakes of the above-mentioned type, which permits the adjusting of the release play without the use of special sensors.
The invention solves this task by providing a control method for controlling an adjusting system of a disc brake having a caliper which reaches over a brake disc axially displaceable on a wheel axle, having brake pads arranged on each side of the brake disc, having an application device for the application of the disc brake, and having the electromotively designed adjusting system which can be controlled by way of the control device, which adjusting system has at least one adjusting device, respectively, on each side of the brake disc. The adjusting device has an electric motor for adjusting the brake pads when brake pad wear occurs. The control method is implemented via a program of the control device, wherein for determining the actual release play of the disc brake, the brake disc with the adjusting devices on each side of the brake disc, is slid back and forth between two axial stops which delimit the displacement path of the brake disc, and the actual displacement path covered in the process is determined, and the actual release play is calculated from that of the actual displacement path, a prestored displacement path calibration value and a desired release play, and is adjusted when a deviation from the desired release play is present or when a limit value is exceeded.
For determining the actual release play of the disc brake, the brake disc with the adjusting devices on each side of the brake disc, is slid back and forth between two axial stops which delimit the displacement path of the brake disc. Then, the covered actual displacement path of the brake disc is determined and the actual release play is calculated from that of the actual displacement path, a pre-stored displacement path calibration value and a pre-stored desired release play and is adjusted to the value of the desired release play when a deviation from the desired release play is present or when a limit value is exceeded.
Thus, for example, when the brake disc is slid back and forth, the electric motor of one adjusting device is first controlled for rotating the adjusting screws in the “enlarge release play direction”, and the electric motor of the adjusting device situated on the respective other side of the brake disc is simultaneously controlled for rotating the adjusting screws in the “reduce release play direction”. After the stop has been reached, the moving direction of the two adjusting devices is reversed until the second stop has been reached. Thus, the brake disc is slid back and forth by the two adjusting devices on each side of the brake disc between two axial stops on the hub, which delimit the displacement path. The amount of the displacement path of the brake disc, which is obtained as the difference of the distance between the two stops and the thickness of the brake disc in this area, can be stored in a memory of the electronic control system.
It is an advantage of this method that the actual release play can be determined without additional sensors.
Another special advantage is a result of the fact that no jamming of the disc brake can take place when brakings are initiated during the measuring operation of the actual release play because the brake disc is in each case moved only from one side of the brake disc, so that, also when the brake pads rest against the brake disc during the measuring, a play is still maintained on the respective opposite side of the brake pad.
When the brake disc is displaced by the wear adjusting devices on each side of the brake disc, for example, by using a decoding device of the EC motors, the actually required displacement path is determined. The actually required displacement path is greater by the amount of the release play than the distance difference stored in the control system because, when the moving direction is reversed, the adjusting device first moves through the existing release play before the brake pad moving ahead of the brake disc up to this moment touches the brake disc. During the measuring operation, the existing release play is always maintained because both adjusting devices are always moved by the same amounts in the same direction.
Preferably, the control device computes the adjusting movements of the brake pads on each side of the brake disc from the determined actual release play and controls the adjusting devices on each side of the brake disc for implementing the adjusting movements for compensating the release play.
It is advantageously possible to determine from sensed changes of the voltage characteristic and/or current characteristic and/or a decoding signal of the electric motors that one of the stops was reached during the displacing of the brake disc.
Expediently, the displacement path calibration value is determined from the difference between the distance of the two stops on each side of the brake disc and the thickness of the brake disc and is stored in a memory as a reference value. Thus, for determining the displacement path calibration value in a simple manner,—by applying both brake pads to the brake disc—the release play can be adjusted to zero; and in this condition, by sliding the brake disc back and forth between the two stops, a measuring of the actual displacement path can be implemented. The distance difference thereby determined without the release play can be stored as a reference value for subsequent release play adjusting operations.
Preferably, the displacement path calibration value is determined after the start of the operation of the vehicle and/or a brake pad and/or brake disc change, expediently on a test stand. However, the distance difference between the two end stops and the thickness of the brake disc in the area of the stops can also be stored in the electronic control system as a fixed value, specifically since, in the area of the stops, the brake disc is subjected to virtually no wear. Preferably, the value is determined by the adjusting system itself when the vehicle is operated for the first time and is preferably regularly updated during the operation of the vehicle; for example, after a start or before the switching-off of the engine. As a result, constructional tolerances as well as operationally caused changes of the distance measurements can be excluded as an error source.
Since the release play measuring operation can be implemented only when the brake is not operated, the measuring operation may also be carried out successively at the different brakes of the vehicle, in which case, during the measuring on each brake, the respective other brakes of the vehicle can also be braked, for example, by means of an EBS system.
Expediently, the axial stops are arranged on the wheel hub in order to further reduce the danger of a jamming in case another braking is initiated during the adjusting of the release play.
According to a variant of the invention, which can also be considered independently, the problem of a constructively simple implementation of the displaceability of the brake disc on the wheel hub is solved.
For this purpose, a brake disc arrangement is created which has a brake disc arranged on a wheel hub, on the outer circumference of the wheel hub cams are distributed. Supporting elements distributed along the inner circumference of the brake disc each reach between these cams. The brake disc, in the mounted condition, is displaceable on the cams of the hub between stops.
The brake disc provided between the supporting elements with one inner extension respectively having a width A is preferably secured in an axial direction by one collar, respectively, which forms one of the two stops.
Expediently, in one of the other axial directions, the brake disc is also secured by securing elements which are arranged at/on the cams of the hub.
The distance between the collars and the securing elements is preferably greater than the width A of the brake disc in the supporting area on the cams of the hub, so that a displacement path is implemented which is greater than zero.
Additional advantageous embodiments of the invention are described and claimed herein.